In an electrophotographic type image forming apparatus, a developing device uses toner to visualize an electrostatic latent image formed on the surface of a photoconductor. The toner thus used for the visualization of the electrostatic latent image is contained in a toner bottle, and the toner is sequentially supplied from the toner bottle to the developing device.
In many cases, the toner bottle has a cylindrical shape having a hollow, and has one closed end portion and the other end portion around which an outlet is provided. Further, the toner bottle has an inner circumferential surface on which a plurality of projecting sections having a spiral shape are provided. Such a toner bottle is disposed in an image forming apparatus such that the axis of the cylindrical shape portion is horizontal.
When the toner bottle is driven to rotate with respect to the axis, the projecting sections provided in the inner circumferential surface guides and transports the toner toward the outlet, with the result that toner having an amount corresponding to the rotation gets out from the outlet.
In the image forming apparatus including such a toner bottle, the toner in the toner bottle is likely to be aggregated and adhered to the inner wall of the bottle, so that it is impossible to use the toner fully. This is problematic.
In order to avoid this problem, Patent Document 1 proposes that a lining layer made of a fluorine resin is provided on the inner surface of a toner container.
The toner container is manufactured by winding a fluorine resin film on the outer circumferential surface of a container main body and further winding paper thereon. Hence, such a toner container has a problem with its strength.
Meanwhile, Patent Document 2 proposes that fluorine-based resin particles are adhered to the inner wall of a toner bottle and a stirring member.
Specifically, in Patent Document 2, the inner wall of the toner bottle is coated with vinylidene fluoride polymer particles, tetrafluoroethylene polymer particles, trifluoroethylene polymer particles, fluoroethylene polymer particles, or the like, each of which has a primary particle average diameter of approximately 0.3 μm.
It is understood that this makes it difficult for toner to be adhered to the inner wall of the toner bottle, thereby preventing the adhesion and aggregation of toner.
As an alternative way, there is a method of adding an external additive such as colloidal silica or a flow improver to the toner.
For such an external additive, Patent Document 3 proposes an external additive made of fumed silica that is surface-treated by using fluorine-containing silane coupling agent and hexamethyldisilazane. Such external additives improve flowability of toner, thereby preventing the adhesion and aggregation of toner.
Patent Document 1: Japanese Unexamined Utility Model Publication “Jitsukaisho 58-38161 (published on Mar. 12, 1983)”
Patent Document 2: Japanese Unexamined Patent Publication “Tokukaihei 8-110691 (published on Apr. 30, 1996)”
Patent Document 3: Japanese Unexamined Patent Publication “Tokukai 2004-144854 (published on May 20, 2004)”
However, in an image forming apparatus carrying out fast image formation, the aforesaid technique of Patent Document 2 cannot sufficiently prevent the aggregation and adhesion of toner.
In recent years, as image forming apparatuses become capable of fast image formation, characteristics of toner have been modified. Specifically, toner is modified to melt at a low melting point such that a fixing device quickly fixes the toner onto a recording sheet. This decreases heat resistance of toner, and the toner becomes therefore easily reactive with the inner wall of the toner bottle. For this reason, toner in the vicinity of the inner wall of the toner bottle is easily adhered to the inner wall.
The technique of Patent Document 2 has no problem in the case of toner used in an image forming apparatus carrying out slow image formation, but cannot sufficiently prevent the adhesion and aggregation in the case of an image forming apparatus carrying out fast image formation.